Salicylic acid (SA) is a phenolic phytohormone that acts as a key regulator of the signaling network in plants under biotic and abiotic stresses. Also, SA exerts stimulatory effects on various physiological processes to plant growth and development. In this research, valerian, chicory, withania and purple coneflowerplants were transferred into anaeroponic system where the effect of SA was investigatedon some plant characteristics under greenhouse conditions in an experiments. The plants were foliar sprayed with SA (0, 50, 100 and 150 mg l-1)at 20, 40 and 60 days after transplanting (DAT).Results showed thatthe highest chlorophylla+b,carotenoid,plant height, root length, root volume,number of leaves per plant, root fresh weight, root dry weight, shoot fresh weight and shoot dry weight were obtained from 150 mg l-1SA in all the studied medicinal plants. The results revealed that the exogenous application of SA in the aeroponic system increased the root fresh weight, root dry weight, shoot fresh weight and shoot dry weight of chicory, withania, valerian and purple coneflower plants.Also, the studied medicinal herbs grew well in the aeroponic system
